Rule of Thumb Accuracy

[BigBro74]

One of my 2bbl stock car engines (13:1, 4.155x3.5 23 deg. iron head, flat tappet SBC) has an Isky cam recommended to me by Ron Iskendarian for the engine (which also fits 128 rule exactly- go figure). I have the engine modeled up in dynosim so i thought i would try the iterator for cam specs using best area under power curve (3-7000rpm) as my test parameter.

248/252 @.050"
.359"/.359" Lobe Lift
105 LSA

Mike thank you for the recommendation.
I am sure you may like to know that you are very much in the same ball park- a few things though, the engine is a 4412 carb,1-3/4 full length headers, super vic intake, basic ported SPII heads 265 intake 185 exhaust( ex) @ .5 lift type deal on hoosier e mod tires 3200 lb car. 6.66 rear gear on the banked 1/4 dirt tracks.they usually run them to about 7000 before they lift.
J

[CamKing]

Mike thank you for the recommendation.
I am sure you may like to know that you are very much in the same ball park- a few things though, the engine is a 4412 carb,1-3/4 full length headers, super vic intake, basic ported SPII heads 265 intake 185 exhaust( ex) @ .5 lift type deal on hoosier e mod tires 3200 lb car. 6.66 rear gear on the banked 1/4 dirt tracks.they usually run them to about 7000 before they lift.
J

That was just my "Rule of Thumb" guess.
The only thing in your specs that throws me, is the Super Vic Intake. Everything else is like the 1,000 other 4412 circle track engines.
I would normally not recommend anything bigger then a Vic Jr, for your RPM range, so I'm not sure what I'd change, to make your manifold work. Maybe run a 99 ICL ?

[David Vizard]

Mikey,

Thanks for the posting swing back to tech instead of ******

Let me continue this with another couple of comments on the effect of LCA changes.

Ever had an engine on the dyno and when you do cam swings the torque numbers don't change that much? In many cases this is due to the fact that the LCA is too wide. The nearer correct camshaft events are for the cylinders/heads concerned the more critical the timing is. The reason is roughly as follows:- If say advancing the cam brought the intake timing to a more favorable spot then the exhaust got worse. Retarding the cam goes the other way - worse intake events but better exhaust. There is also the effect on scavenging brought about by moving the overlap but that simple reasoning is as good a simple explanation as any. If the LCA is precisely what the engine wants the cams advance/retard position in the engine becomes far more critical.

Footnote here. Don't take the cam cards cam setting as the be all and end all. In reality it is just the cam companies best guess. It's worth keeping in mind that the cam timing for optimum output is not a function of the cam but a function of the cylinder displacement and the intake/exhaust flow ratio during the overlap period.

DV

[David Vizard]

So for a 355 SBC, 23°heads, 10.5 compression, 6500RPM peak it comes out to 108LSA is the contention here that no way could a 110 or 112 etc cam make more power than the 108 no matter what the open/close events are?

Its not a yes/no answer here and I have to get some work done as at the moment I am able physically to do so. I will address your query in a later post here.
DV

[David Vizard]

i don't understand why you wouldn't come up with a method that determined ICL and ECL separately.

I have, it's called TorqueMaster (see page 2 of this thread)
DV

[David Vizard]

David,
I hope I can communicate my question to you properly. Can you provide some analysis of why various engines seem to like cam profiles that they do

For example, based on my testing of SBC, they like this cam profile and here is why. Iron heads with this CSA , valve configuration, compression etc.... made the best power with this cam profile and here is why. SBF liked something else and here is why I believe they like what they do...

What are the trends you saw during testing that caused you to come up with your 123 formula.and then determine that you can tweak it for other engine platforms.

I want to understand your logic in making the formula.

John,
This is going to be a long long post if I do it. We will be getting together at my place later in the year so we can cover that and any subsequent questions you may have.

See you down the road,
DV

[David Vizard]

Jon, either you must not have read my very comprehensive post on page 2 or you simply cannot read. Either way I cannot afford to waste time on someone who cannot even answer a simple yes or no question.
If I researched my books to the level you absorb plainly a posted responses I would have been out of business 50 years ago. Please don't waste my time unless unless you have a really well thought out response that answers answer directly the points raise on my page 2 post.
DV

I responded to your complaint about being criticized, I will take your attempted defection as an admission that my point is correct.

Jon,
This is nothing short of proof you cannot focus on giving a straight answer to even a yes/no situation.
Your point is absolutely not made. In fact you have proved mine. Namely that giving a simple answer to a question rather than posing another in it's place seems impossible. Please try and address the questions I have asked directly without any unnecessary padding.

Please -please -please go back and answer some of the questions I have asked of you without putting any superfluous comments in.

DV

[Stan Weiss]

i don't understand why you wouldn't come up with a method that determined ICL and ECL separately.

I have, it's called TorqueMaster (see page 2 of this thread)
DV

David,
Maybe a picture will work better than words.

Stan

tmc_s.gif

[David Vizard]

www.hotrod.com/articles/camshaft-shooto ... explained/

Can someone with formulas at hand see how this compares ?

"Engine size divided by the number of cylinders.
That number divided by the intake valve diameter.
That number multiplied by .91.
128 minus that number equals LSA."

370/8=46.25

Intake valve diameter? 2.02
46.25/2.02=22.896
22.896*0.91= 20.835
128-20.835= 107.165

Intake valve diameter? 2.05
46.25/2.05=22.560
22.560*0.91= 20.530
128-20.530= 107.47

As usual for this type of engine, it all depends on what the driver wants.
The lower LSA cam seems to have the most power of those tried.
Looks like something around 105 would be the next thing to try.
The 107 (as predicted by 128) didn't work so well in this case.

westec_370.jpg

This is a good test except none of the cams were power timed to find the optimum ICL.
DV

[SchmidtMotorWorks]

OK Jon, with all that's been said here can you give me a simple yes or no answer to the following question?
From what I have outlined here do you see any justification as to why I should spend time to modify my simple 128 formula to do the things you so fervently think it should do to be of any value to the end user.
DV

I think you should not make statements like the one posted below when all you have is a 2 input formula.

Have you ever given any thought to the most important factor is for camshafts?
Is it duration, lift, lobe center angle?
No!
I'll tell you the most important thing you can know about specing out cam it's one hundred and twenty-eight.
Don't bother calling the cam companies they won't know about it

It is good for a laugh though.

[David Vizard]

And at the end of the day some guys will over think it, and has always been about RESULTS. But some of you guys will pick those apart as well.

This shit is laughable.

Yep, most people could go with "the magic LSA is always 107 on a high performance street SBC" and few would complain about the results.

No magic beans required.

Ok Jon. You win. Just like Comp grind everything on the de facto 110 LSA and call that good. Is that YOUR answer? If it is you are full of shit. Because I know from decades of doing this shit, that 110 is NOT a good LSA for MOST OE cylinder head architecture. But bet your sorry ass, if I call Comp (add in your favorite cam grinder here, could be Howard's because they have now adopted the stupid 110 LSA as de facto, as has Lunati AFAICT) they'll pick a 110 LSA for every single combo I can come up with.

AND THAT IS THE ISSUE. YOUR DE FACTO IS NO BETTER THAN WHAT DV HAS AND DV HAS HIS SHIT AS TIGHT AS ANYONE ELSE IVE SEEN.

This is like the 50* seat thread. Fucking people want a set, hard rule as to when to use it and there isn't one. Just like this rule of thumb rule. The stupid long haired school types who never have to use this junk poo poo it and the guys who don't give a shit how much time you spent at school don't care what you think.

When Jon Schmidt actually can post up some shit that he has actually BUILT, HIMSELF then I might give a shit.

Statsystems,

I hate to ask but ---um --- well ---- ah like --- did you have an opinion here???????

[David Vizard]

All of this is blah blah blah to me really, but others may find some value, and more power to them!

But a quick question for Mr. Vizard, if your presence here is to simply help the common man, and NOT to constantly promote your self, books and seminars. Why don't you help out with your thoughts in the many cam related threads going on currently, or to any other of the various thread topics?
No matter your views, I think they would be more welcomed, and less harshly criticized, if that was the case......?
I have NO dog in this fight, just some casual observations from the grandstands.

Warp,
A reasonable question here. Very often when reading posts I see an avenue that is being wrongly addressed and rather than march in with my dyno findings and throw them in the face of those believing otherwise I leave it for 3-4 months and then start a thread on that subject. This seems to be the way to go to ease the effect on many ego's. Also threads wander off subject very quickly unless someone take at least an interest in guiding them down a useful road they end up defeating the original object.
DV

[RevTheory]

Jon thinks that actually building an engine is beneath him but loves to hide behind his supposed NDAs. When do you remember pinning Jon down on an actual number?

He prances around talking about peer review but he'll never post up a number for peer review.

[David Vizard]

Back to some useful tech here.

Lets say you are looking at two cams which are close to what you feel from experience/calculation or what ever are close to the required LCA. What are the consequences of either choosing a little too wide a LCA (say up to 2 degrees) than too tight a LCA (again say by 2 degrees).

A healthy 4 figure number of dyno tests has shown that in the case of a performance engine the torque drops off faster when the LCA is too wide far faster than when it is too tight.
In fact the track time of a cam 2 degrees too tight shows near zero lost of performance. Where it does show less favorable is in the idle quality and vacuum pulled. Also the motor comes up on the cam more abruptly.

So when making a choice you need to err toward the tighter LCA rather than the wider one.

DV

[RevTheory]

I had to hold my nose and close my eyes when I bought my first cam that Denny from MM&S did clear back in 2003. I checked my email for two days with one eye open and it came back with 280 single pattern degrees on a 106 for a 10:1 383 using AFR pre-Eliminator heads (2.02x1.6 valves).

I reluctantly called Comp and ordered it up and they did their usual routine of trying to talk me into one of their ubiquitous shelf-grinds on a one-size-fits-none 110 LSA with what, 8 degrees of exhaust bias without asking me a damn thing about the engine.

I stuck to my guns though and ordered the cam. I dynoed the engine in Reno and the little thing broke 400 ft/lbs at 2,750 rpm and that ain't bad for 2003 cylinder head tech. Made 486 HP just shy of 6,000 rpm and that was basically an assemblers engine. No fancy tricks.

You know the shop owner (Dave something or other that I've never been able to pronounce right) and he was talking a little bit of shit about how the cam was all wrong for the truck and it'll never idle because it's on a 106 and the torque curve will be completely unusable, etc., my machine shop said the same thing.

He pulled it down for its first 4,500 rpm plug cut, saw the torque output, set back in his chair and rubbed his bald head and said, "now what did you do with the cam? This is going to be a dynamite truck engine."

Now granted, it was a nasty sob at idle but it cammed up in a heartbeat and hit hard from a wot stomp.